I love history and electronics. Where do the terms ‘Discharge’ and ‘Charge’ come from? Enjoy this little treasure….
Electric Vocabulary
Lipo Battery Disposal
I need to know how to dispose of LiPo battery that has swollen due to an overcurrent.
There are two issues.
1. We want to discharge the battery in such a way as there is minimal risk of fire during the discharge and later when the battery is in the recycle or trash bin.
2. We want to dispose of the depleted pack in a recycling container.
The first thing to do is remove all potential from the battery. We do this with an 1157 light bulb (Brake/Marker type bulb). It’s handy to use because it gives an indication of ongoing discharge by emmitting light and doesn’t tie up one of my ever working chargers. We have our bulb wired with alligator clips and a switch to choose between one or both filaments. I don’t remember what the draw is per filament, but we considered that a small cell would be more safely discharged at a lower rate than a larger cell. When discharging a large cell, we set the switch so both filaments burn. We use an ammo box as an oxygen poor fire safe to do this, since we are indoors and we’re working with a suspect pack in the first place.
This is allowed to burn until the bulb is out, then allowed to set connected to the bulb until the following day. This way we are 100% certain the pack is completely exhausted.
Next we solder together the leads on the pack. Just in case any recovery or bounce back of capacity in the pack were possible, it is constantly discharged through the short. There should now be no chance of any kind of arc or spark starting a fire in the recycling container. Being that the pack is completely empty, there should not be any energy present of any kind.
Federal law (49 CFR 173.185) states lithium type batteries must be individually packaged in non-conductive material and transported to a “permitted” recycler. In our shop, we use Call2Recycle (also known as RBRC 1-877-723-1297). They provide free recycling materials and processing. A bag is provided for each pack, we wrap the back in the pack, seal it, drop it in the box. When the box is full, we contact UPS for a free pickup and delivery to the recycling station. Any local battery seller should have this capability on site. We accept lipos for recycling at Radical RC.
Help finding a Call2Recycle RBRC Recycling Location near you.
There may be other safe and accepted ways of doing this, the above is how we handle it at Radical RC.
Converting A Model From Lipo to A123 (LIFE) Cells
Chris from Michigan Asks;
Hello Dave,
I would like to power my Ryan with A123 cells. I have been using a 9s 4p 6000mah Lipo pack to power a Hacker C50 motor.
If I understand things correctly, I believe that I need 4packs 6s 2300mah to equal the same watts and flight duration as the Thunder Power packs that I have been running.
Because of the cost of these A123’s, I want to be sure that what I am ordering is correct!
Chris,
To match duration of a 6000mah Lipo, you’ll need at least 6000mah in A123 which will be 3P. You’ll actually be a little over as the 2300mah A123 cells actually test most of the time around 2200, at 3P you’ll have 6600mah which should result in slightly more flying time.
I assume your 6000mah lipo is made up of 1500mah Parallel packs. So, 4 1500’s in parallel = 6000mah.
If what you really meant was your running 6000mah cells, 4 in parallel, then your pack size is 24000mah which would be about 11P or 11 A123 in parallel. I am not thinking you meant you had a 24000mah pack.
If your running 6000mah total in the airplane, and are thinking of running A123 in 2P for about 4400mah real world, this may be just fine. I generally only use the top 60% of a Lipo (70% max) on a routine basis. 60% of 6000 3600mah, 70% is 4200mah. I’m more comfortable running A123 cells a little deeper than Lipo’s as the risk of hitting BEC cut off cause me less worry. (Hitting BEC cut off is hard on Lipo’s) So, running a 4400 A123 down 80% is 3200mah. So, a 2P A123 should get close to the Lipo in actual use. However, your not running as much cushion between a solid end of flight habit and the bottom of the battery.
For matching running voltage, you’ll need 10 to 11S A123. I’d probably go to 11. At 12S, you’ll definitely have 3-4 more running volts. It will be like 9.8 Lipo or something like that.
To do conversion at nominal voltage, (# Lipos * 3.7) / 3.3 nominal of A123 = cell count.
To do conversion at full voltage: (# Lipos * 4.2) / 3.6 full voltage of A123 = cell count.
Nominal conversion is: 9 Lipo = 10.09 A123 cells
Full voltage Conversion is: 9 Lipo = 10.5 A123 cells.
Since you do most of your flying between full and nominal voltage I lean towards the full number for this estimation. 11 is the best choice. 10 you might notice a slight decrease in performance by your motors KV * volt reduction of the 10S pack. Right in the front of the pack, the 9S Lipo is 37.8v. Right in the front of a 10S A123 your full voltage will be 36v. So, KV X 1.8 = drop in top rpm. If your running a 500kv motor, that’s 900 rpm.
If you go with 11 cells, you’ll be starting out at 40.4v meaning your over the Lipo voltage by about 2.6v. So, you pick up (with 500kv motor) 1300 prop rpm.
Either choice means to get back to exact performance you had on Lipo you may need to alter the prop slightly, maybe an inch more pitch for the 10S A123 and an Inch less pitch for the 11S A123 or something similar to re balance things back out.
So, on balance, not knowing everything about the model and power system, I’d lean towards 11S. If you go 12S as your proposing, you’ll likely end up way over on RPM and Watts from where you were with the 9S Lipo pack. Important considerations here are if you mind a little more or a little less power (if the ESC minds more amps/voltage) and if you would need to change props, is there a convenient prop up or down that would suit the model and flying preferences. For example, if your running right at the edge of the ESC at this time and didn’t want to upgrade it, a slight decrease in power is acceptable, 10S becomes the obvious choice.
Another consideration not taken into account above is there can be a wide variation in quality of Lipo’s people are using out there. (not picking on Thunder Power, remarks for general readers of this post) Your current pack which may be performing just fine for the application may be worn and not really up to snuff compared to the original new condition. Thus if the current lipo has more voltage depression than it should, an A123 10S pack depressing less by some significant amount, could end up taching and watt metering out higher than the battery you are now using.
Skin Effect – Why Many Fine Strands Are Better
Skin Effect Explained. Why many fine strands (the finer the better) are better than fewer (or one) strand(s). Hobby wire (good hobby wire) is more costly than your garden variety speaker and automotive wire because of it’s higher strand count and surface area. Particularly between an ESC and Motor. Read more:
Twisted-wire Conductor & Skin Effect”
Wire Caculator AWG to Curcular Mils
A calculator published by the Mogami company. It is helpful to understand wire size a little better. For example, a solid core 22 gauge wire has a different overall diameter if it’s 16 strand or 32 strand or 198 strand. Don’t get fooled into thinking AWG is the diameter of your wire regardless of strand count. Actually as the strand count of multi strand wire gets higher and higher, the overall diameter of the cable gets smaller. Think of it this way, the smaller the wire, the smaller the air pockets or gaps in the bundles of copper become. In other words the wire bundle becomes more and more dense. I run into people from time to time that think it’s as simple as measuring OD of the bundle, some get quite insistent defending their theory. We’ll perhaps they are just wishful souls dreaming about how great the world would be if it was as simple as they wish it was? Below is a handy site to help you figure out what size your wire (or any wire we sell) really is. It’s not super simple but you can work it out and learn something.
If you run across any interesting calculators please forward them to me.
Checking A123 RX Packs For Recharge Point
A123 RX Packs can be tricky to deturming how much is left in the pack by checking voltage alone. Variations in connectors and length of wire can have a big impact on actual volt readings when loaded. Using an RRC1000 digital voltmeter with load capability of 0.0A, .5A, 1A and 1.5A we get the following results measuring a 2300 2S RX pack with 6″ 20 g silicone JR pigtail and the included 22 guage battery checker pigail with the meter. Note: the meter (which ever you are using) is reading the voltage on it’s board, not at the pack. The voltage at the pack will actually be higher by the voltage drop across your checkers connector, pigtail, checker/pack connector and the pigtail on the pack. Here are the results we measured at varous loads. Room temperature was 74 degrees F, each load held aproximately 5 seconds before reading taken.
| State Of Charge | No Load Resting Voltage | .5 Amp Load | 1.0 Amp Load | 1.5 Amp Load | 40% | 6.58v | 6.37v | 6.18v | 6.09v | 30% | 6.52v | 6.38v | 6.17v | 6.06v | 20% | 6.45v | 6.32v | 6.19v | 6.08v | 10% | 6.38v | 6.25v | 6.14v | 6.04v | 0% | 5.43v | 5.19v | 5.08v | 4.98v |
|---|
As can be seen from the data above, at some loads, the pack actually increased slightly in voltage as we went down even though the overall trend was lower in voltage. Note this test was not over a multitude of packs which would be more accurate and likely nuetralize the unexpected results mentioned.
Notice how little the pack is falling off in voltage and that the biggest consistant drop is in the resting voltage column, not a result I expected.
Notice the results at 0% capacity remaining as measured by my charger/discharger. As it is important to understand the context of the data and how I was checking the voltages, it is also important to understand the context of the data and how I was discharging the pack in 10% steps until empty (more explanined below) All discharges to make this chart after the initial 60% discharge were at 1.1A and in 230mah steps. The discharge harness was made from 22guage wire, 24″ long and plugged only into the JR output lead on the pack. Even though after 5 seconds of holding the load, I got the voltages above on the 0% line, putting the pack back on the discharger and trying to discahrge it some more resulted in the pack falling off to the 4V cut off (the empty point) in only about 10 to 15 seconds. Yet, I was still able to measure almost 1.5 higher than that when the pack had come off the first discharge to empty and been allowed to set for only 10 minutes before I measured anything. We can see that a wide range of voltages over 5 to 15 seconds with differing loads were all the same thing – EMPTY! Pay attention to the context of everything or you’ll get fooled! Because the context of how you are checking the voltage has such an impact on the reading, you should check your packs the same way every time with religious zeal.
A123 Systems cells ability to hold a strong voltage under load all the way until they are empty is one of the primary reasons they are so popular as RX packs, yet it is the very reason they are somewhat more challenging to voltmeter check from flight to flight.
To devise your own chart, cycle the pack to deturmine it’s actual value (ours was 2250), recharge, then set your chargers limiter to 60% of the actual value (ours was set to 1350) and discharge at capacity/2 (we used 1.1amp for our pack). After you’ve discharged it to this point, take the reading with the equipment and through the switches or whatever you have installed in your ship. Now you will know the readings at the 60% discharged (40% remaining) point. This is where you should be recharging any mission critical pack such as a TX or RX pack. To arrive at another row of data aproximately 10% further down in the pack, we simply set the limiter to 230mah and repeated the discharge. Repeat for each line of data you’d like to collect. You could start from full and discharge in 230mah steps generating data for 100%,90%,80% & etc….. Science, don’t you love it!
It would be my advice to think about making your own chart so you can learn something and become firmiliar with the voltage drop across all the gear in your model. You’ll be measuring the pack across a switch harness in most cases which will give you lower voltage readings than these.
General practice should be to taxi the model back to the pits, and before you’ve turned it off, plug your loaded volt meter in, turn off the model and take your reading immeadiately. Note your own chart for the correct cut off voltage and always recharge at the 40% remaining point. Flying below 40% is dipping into your reserves and should be avoided for any mission critical pack.
2.4GHz: Is it all it’s cracked up to be?
Artical at Model Airplane News written by: Dave Horvath
This is an important artical explaining some of the reasons why 2.4ghz has issues. People can be counted on to always presume that newer is better. I was very late to start using 2.4ghz due to reliability issues. With about 1/3 of our hobby being replaced by newbies every year, it makes perfect sense that not many lifers are left that remember what standards of reliability we had acheived with 72mhz. Dave Horvaths artical is important reading to gain a broader understanding of how things work.
Dave Thacker
Doc Brown Power Supplies Checked For Possible HAM Usage
I’ve had several inquirys wondering if these power supplies can be used for Ham purposes. A local Ham checked one out and writes:
Dave …
I’ve used this with a Yaesu FT-817 (5 watt, around 2 amp), scanned across the bands, and found several places where there are “birdies” or RF that can interfere. It seems to be on the power line, since I had no antenna attached at the time.
1.805 MHz, 1.784, 1.685, etc. These likely come from the switching mode, since the signal disappears when the power supply is unplugged. I would suggest that HF ( from 1.8 MHz to around 30 MHz) may be usable on some bands, but not all. At VHF and UHF frequencies it is well filtered enough to use, that is at 140 MHz and 430 MHz. With its current level it could run a 100 watt repeater at VHF nicely.
Of course, this isn’t at the same level evaluation as someone at the ARRL or FCC labs, since I have not measured the actual level of signal involved. I can not see anything on the Tektronics oscilloscope, but it only goes to 2 mV/cm. A signal at that level would be rather loud.
John Hepner KA8ZSB